Embodiments of the invention relate to a projection display and a method for displaying an overall image.
The projection of dynamic image contents on a screen or as a virtual image with a digital liquid crystal-based imaging system is based, according to conventional technology, on projection devices having a mapping optical channel or three channels whose optical paths unite in front of the projection optics for realizing color mixing.
In particular, US 2009 323 028 A1 shows pico projectors illuminated by LED in a color sequential manner. Further, US 2009 237 616 A1 describes a projection display having three color channels combined in front of the projection optics.
However, if the dimensions of the systems known in conventional technology are reduced for realizing miniaturized pico projectors, luminosity losses of the projected image result. Miniaturization of known projection systems is only possible in a limited manner due to the limitation of the transmissible light flux through the small surface of the imaging system existing in these systems. This connection is determined by the optical principle of etendue conservation. The etendue or light grasp of a light sourceE=4πn2A sin Θresults from its luminous surface A, the half angle of divergence Θ and the refractive index n and remains constant with an ideal optical mapping. Real optics increase the etendue or reduce system transmission. Thus, a minimum object surface is necessitated for a source having a given luminance for a minimum transmissible light flux within a projecting optical system.
It is a general problem in single-channel projection systems that due to optical laws (e.g. natural vignetting, mapping errors), together with this surface to be mapped, the system installation length also increases to the same extent, which makes miniaturization more difficult.
One solution for this problem is described in DE 102009024894. There, a projection display having a light source and regularly arranged optical channels is described. Due to a slightly reduced center pitch of the projection lenses with respect to the imaging structures, an offset of the respective imaging structure and the respective projection optics increasing towards the outside from the array center results, so that superposition of the real individual mappings or images results at a finite distance. Due to the partitioning into several channels, it is possible to reduce the distance between the imaging structure and the projection optics, i.e. the installation height, so that miniaturization is obtained simultaneously with other advantages.
However, problems occur when the above systems are used in connection with curved or tilted projection surfaces. All the above-described systems are only implemented in connection with the use of planar projection surfaces. Generally, the problem is the front projection of an image across greatly changing projection distances or tilted, curved surfaces, and free-form screen geometries while ensuring high contrast and sharp mapping. Sharp imaging can be obtained for a tilted planar screen by extensive tilting of object and projection optics according to the Scheimpflug principle. However, this known approach fails for curved projection surfaces. Tilting again increases the necessitated installation space. If even adaptivity to different degrees of tilting is to be realized, this necessitates mechanics for realizing the tilting between imaging structure and projection optics, which opposes the desired miniaturization and low production costs as well as robust construction. An increased f-number could solve the problem by increasing the depth of focus, but such an increased f-number is also accompanied by lower light intensity causing other problems and additionally also opposing miniaturization, since the problem would then be shifted to the light source.